AS YOU BEGIN PLANNING your app's design, set aside the pixel-by-pixel nitty-gritty of your app's buttons and colors and icons. Let go of the look of your app, and consider how it works—its big-picture organizational design. When you pull way back to look at your app from a high level, you'll see that its essential operation depends on easy movement from screen to screen. All but the most simple iPhone apps are collections of multiple screens, each one dedicated to an individual task or to specific content. How you choose to string those screens together determines how people will steer their way through your app, and it's one of the most fundamental choices you'll make when planning your design.
This chapter tours the iPhone's navigation styles to explore the options for arranging your app's content and tools. Specifically, you'll get an overview of the several prefab organizational approaches that are baked into the iPhone SDK, the coding toolkit developers use to build apps. You're not obliged to use any of these methods to build your app—you'll explore custom alternatives in Chapter 6—but leaning on the built-in navigation models gives your audience a structure that's instantly familiar. It helps your app blend both visually and organizationally with other apps. Blend in? Of course you want your app to bloom like a unique flower, and it will, but you're not operating in a vacuum. Designing for the iPhone, like designing for any platform, means respecting the norms and conventions of its operating system. An iPhone app should look like an iPhone app. Adopting one of the stock organizational structures (and choosing the right one) is a fundamental way to do that.
The best apps have a design that fits in as if designed by Apple itself. That familiar feel is helped along by savvy use of the standard navigation methods and interface controls. This chapter begins to explore these standard presentation methods, starting with navigation and organization, and the next chapter surveys individual controls. The goal of these two chapters is to help you design apps the Apple way. Before we get started, here's one recipe for doing that—at every interface decision point, ask yourself this question:
Apple co-founder Steve Jobs built an entire brand around impeccable taste, quality, and ease of use. There's much to be learned by carefully studying Apple's own app designs and following the company's example. At the simplest level, Apple makes pretty things; if you're going to ape an aesthetic, Apple's a good choice. (That's true not only for what Apple puts into its built-in iPhone apps, but for what the company leaves out, too. As you've seen in previous chapters, tapworthy apps winnow features and limit controls for efficiency and ease; Apple's apps are refined examples of disciplined moderation.)
But this is about more than just style and looks. Apple's design decisions set the standard for the device, the frame in which all apps are considered and understood. The iPhone is like a celebrity red carpet: there's plenty of room for individuality, but ultimately you still have to wear an evening gown. Don't let your app wear a hobo costume to a formal ball. Following the dress code makes your app consistent with other apps, which in turn makes it easy for your audience to make sense of your app and understand how to make the thing go.
The remarkable consistency of third-party interfaces on the iPhone is a significant reason for its ease of use. This level of app affinity is unusual for any software platform, especially one that's so new, and it didn't happen accidentally. As a company, Apple is famously opinionated in matters of design. Rather than leave developers' interface choices to chance, the company created detailed rules for designing iPhone apps and codified them into a document called the iPhone Human Interface Guidelines, commonly known as the HIG. The HIG delivers Apple's design commandments, the company's definition of what it means to be a good iPhone citizen. Most operating systems, including Windows and Mac OS X, have a similar HIG to outline software best practices and behaviors. Like the device itself, however, the iPhone HIG feels different than that of other operating systems. It's an accessible read for regular folks, not just developers and is an essential document for everyone involved in your app's design. Download the HIG at http://developer.apple.com/iphone.
The HIG surveys the iPhone's toy chest of standard controls and views and explains the right way to use them to do what users expect them to do: use this interface gizmo to do this, use that widget to do that. This chapter, along with the next, introduces those gizmos and widgets, building on the HIG's basic concepts. These chapters offer examples and best practices, as well as warn you away from problem areas so that you can make smart decisions about when, where, and why to use the various controls and navigation options.
While the HIG focuses on interactive behavior more than visual design, it nevertheless has visual implications. The standard collection of buttons, controls, and views that Apple provides in its code toolkit strongly suggests how things should look on the iPhone, not just behave. The controls come in standard colors, many lodge automatically in certain parts of the screen, and the absence or inclusion of certain types of controls in the SDK implicitly encourages certain design choices. Apple doesn't provide checkbox controls, for example, so the iPhone's checkmark accessories and on/off switches become the norm instead (see Table Views Are Lists on Steroids and Yes and No: Switches respectively).
Pay attention to these guidelines. More than just informed and battle-tested suggestions, Apple's interface guidelines are also criteria for App Store approval. Misuse a toolbar icon or bobble an activity indicator and you risk having your app kicked back to you for a fix before Apple's reviewers will accept it into the App Store. Avoid trouble by favoring standard controls in your app and abide by the guidelines in the HIG and in this chapter. Aside from the threatening stick of App Store rejection, there are also some tasty carrots in it for you when you use standard controls. Apple's guidelines reflect the sensibility of the interaction designers who created the iPhone interface, undeniably a bright bunch of people, and the conventions they've developed are good ones. Let's take a look.